The heart of a computer is a magnetic disk drive which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, the boundary layer is swept along by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The depletion of lubricant on disks in a hard disk drive is always a concern when there is movement of the lubricant from a given track to another track or from a macro perspective from one region to another region on the disk. A macro perspective movement may be a movement from an inner radial track position to an outer radial track position. The lubricant may become depleted due to mobility of the lubricant or external influences such as high rotations per minute (RPM), high temperatures and/or head transport. The lubricant will typically be removed from one region of the disk and moved to another, i.e., from the inner track radial position to the outer track radial position, or vice versa.
In addition, there is an added problem of lubricant loss via evaporation due to sinking regions within the drive or leakage from the drive. If there are screw holes that are not appropriately sealed, the lubricant may migrate out of the drive to the outside environment due to a concentration effect, i.e., the lubricant may migrate from an area of higher concentration to an area of lower concentration.
Lubricant depletion can also be due to electrostatic voltage differences between slider and disk, i.e., the slider disk pair act similar to a capacitor. Lubricant is slightly electronegative (less than 0V) and comes off the disk easily if a positive voltage is applied to the slider body. Voltage differences occur in HDD's due to spindle motor charging up (tribo-charging) and due to contact potential differences between slider and disk. The contact potential (or surface potential) arrives from a work function difference between the two materials (slider and disk). Typically, the surface potentials in current disk drives is about 0.4V which drives lubricant depletion. Offsetting the surface potential may reduce lube pickup. However, lubricant passivates the slider and changes the surface potential, i.e., by measuring the surface potential over the entire disk one can map the regions of lube depletion. This could give an additional trigger event to open the lube reservoir. Regions of large lube depletion can be triggered by these 3 events: 1) surface potential change 2) clearance change 3) friction change. In regions of large lubricant depletion, a slider disk contact would also yield much higher wear rate. The disk can then be mapped out for (single or multi-track) disk contact potential to find regions of lube depletion. This would allow a trigger for opening the lubricant reservoir.
Therefore, it would be beneficial to have a system or method to replenish the lubricant at the depleted positions, i.e., any region where there is a high rate of lubricant depletion.